The localization and mapping of mobile devices is a hot spot in the field of robot. There has been a practical solution to the self-localization of mobile devices in known environments and mapping with known locations of robots. However, in many environments the mobile device can't be localized by using global location system, moreover it is difficult or even impossible to obtain the map of the mobile device's working environment in advance. Hence the mobile device needs to build the map in a completely unknown environment under the condition that its position is uncertain, and use the map to locate and navigate autonomously. This is so-called simultaneous localization and mapping (SLAM).
According to the simultaneous localization and mapping (SLAM), the mobile device identifies characteristic indications in an unknown environment by utilizing sensors in the mobile device, and the global coordinates of the mobile device and the characteristic indication are estimated according to the relative position between the mobile device and the characteristic indication and the reading of the encoder.
So far, the most common exiting positioning techniques of automatic walking robots or devices are:
(1) GPS positioning; the basic principle of GPS positioning is based on instantaneous position of the satellite moving with high speed as a known starting data, and using the method of spatial distance resection to determine the location of the point to be measured.
(2) bar code positioning mode. To convert the bar code compiled according to certain rules into meaningful information, it is necessary to go through two processes of scanning and decoding. The color of the object is determined by the type of light it reflects, the white object can reflect the visible light of various wavelengths, the black object absorbs the visible light of various wavelengths, so when the light emitted by the bar code scanner light is reflected on the bar code, the reflected light is irradiated to the photoelectric converter within the bar code scanner, and the photoelectric converter converts reflected light signal into the corresponding electrical signal on the basis of different strength of the reflected light signal. According to different principles, the scanner can be divided into three types: light pen, CCD and laser. After being output to the amplifying circuit enhancement signals of the bar-code scanner, the electric signals are transmitted to the shaping circuit to convert the analog signals into digital signals. The width of the black bars and black bars is different, and hence the duration of the corresponding electrical signals is different. Then the decoder determines the number of bars and nulls by measuring the number of pulse digital electrical signals 0f 0 and 1. The width of the bar and the empty is determined by measuring the duration of the 0,1 signal. But the obtained data is still chaotic, in order to know the information contained in the bar code, it is necessary to convert the bar symbol into the corresponding number information and character information based on the corresponding coding rules (such as: EAN-8 yards). Finally, the details of the items will be identified through data processing and management by computer system.
The above-mentioned positioning technique applied in automatic walking robot or automatic walking equipment is relatively complex, each with different shortcomings:
1. GPS positioning is not practical due to signal problems in the room.
2. The bar code positioning mode is limited in usage occasions due to the fact that the bar codes are easily polluted and cannot be read.
Positioning and navigation technique of the mobile robot in the indoor environment has the characteristics of high precision and complicated environment for positioning, so the methods above are not applicable.
RFID (Radio Frequency Identification) radio frequency identification is a non-contact automatic identification technology, which identifies a target object automatically and acquires related data through radio frequency signal, without manual intervention, applicable in various severe environments, hence the RFID technology can identify high-speed moving objects and multiple labels simultaneously, and the operation is rapid and convenient. Therefore, it is necessary to combine this technology to improve the existing positioning and navigation method for mobile robots.
In the existing RFID-based positioning technique for automatic walking robot, for example, a Chinese utility model patent with application number of CN2013204818.2, discloses a RFID indoor positioning system which specifically comprises a plurality of electronic tags which are arranged in the positioning region in an equilateral triangle mode, and calculates and positions through wireless signal strength. Although the method is effective in locating in the indoor environment and with high position precision, but the shortcomings lies in the need for at least three electronic tags to transmit wireless signals, moreover the arrangement mode of the three electronic tags is fixed as an equilateral triangle shape, so the method is too limited and not very adaptable.
Another Chinese invention patent with application number of CN201080034870.0, has disclosed a RFID positioning system in which the position is determined by reading the RFID tag information which is attached to a certain position of a building. According to the method, it is no need to fix the arrangement mode of the three electronic tags an equilateral triangle shape, but information such as the size of a building needs to be accurately measured, and then the position information is written into the RFID tag through the RFID reader-writer, as a result the operation is complicated, and only by arranging a plurality of RFID tags can the positioning effect be realized.